This invention relates to method and apparatuses for flash welding a pair of workpieces.
In a conventional flash welding method, a pair of workpieces to be welded are movably supported by clampers, and at least one of the workpieces mounted on a movable bed is moved toward the other workpiece by a hydraulic cylinder. A voltage is applied across the workpieces to generate flashes between the workpieces for heating and melting the workpiece surfaces to be joined together. When the workpieces are sufficiently heated, they are upset with a predetermined upsetting force by the hydraulic cylinder. The upsetting force is removed from the workpieces when the welded portions of the workpieces are firmly put together.
In the above flash welding method, the voltage between the workpieces and the movement of the workpieces are respectively independently controlled in accordance with the lapse of time irrespective of the progress of actual welding, so that it is difficult to obtain welds of a higher quality.
During upsetting, the workpieces must be moved toward each other at a high speed to prevent the oxidation of the hot weld surfaces. In order to accelerate a workpiece together with a movable bed for carrying it at a high rate, a large force, such as 5 to 7 kg/mm.sup.2, which is larger than the pressure required for upsetting, must be applied to the movable bed. Since the workpieces tend to buckle when such a high upsetting pressure is applied to the workpieces after the upsetting, the upsetting force must be removed from the workpieces after the workpieces have been upset by a predetermined upsetting quantity. Therefore, the body of the apparatus tends to vibrate during the upsetting process, and the workpieces may vibrate in the cooling process of the workpieces after their upsetting, the vibration having an adverse effect on the quality of the finished weld. Also, when a high upsetting pressure is applied to the workpieces, the apparatus must be heavy and large-sized to withstand the high upsetting pressure.